U.S. patent application number 12/300725 was filed with the patent office on 2010-07-08 for electric compressor.
This patent application is currently assigned to MITSUBISHI HEAVY INDUSTRIES, LTD.. Invention is credited to Masahiko Asai, Makoto Hattori, Takashi Nakagami, Koji Nakano, Hideto Noyama, Takayuki Takashige.
Application Number | 20100172764 12/300725 |
Document ID | / |
Family ID | 40667314 |
Filed Date | 2010-07-08 |
United States Patent
Application |
20100172764 |
Kind Code |
A1 |
Nakano; Koji ; et
al. |
July 8, 2010 |
ELECTRIC COMPRESSOR
Abstract
There is provided an electric compressor that can protect a
component to be protected from heat damage according to a
capability of the component. The electric compressor 10 includes a
compression mechanism 11, an electric motor 12 that drives the
compression mechanism 11, and a control portion 13 that controls to
drive the electric motor 12, incorporated into a single casing, and
further includes a temperature detector 14 that detects a
temperature of one or more components that constitute one or both
of the control portion 13 and the electric motor 12, and a current
detector 15 that detects a current flowing through the component.
When the temperature detected by the temperature detector 14 is a
temperature Td, the current detected by the current detector 15
when the temperature detector 14 detects the temperature Td is a
current Id, and a current corresponding to the temperature Td at a
temperature characteristic relating to the current specific to the
component is a current Ia(Td), the control portion 13 stops driving
the electric motor 12 on the basis of a result of comparison
between Ia(Td) and Id.
Inventors: |
Nakano; Koji; (Aichi-ken,
JP) ; Nakagami; Takashi; ( Aichi-ken, JP) ;
Noyama; Hideto; (Aichi-ken, JP) ; Asai; Masahiko;
( Aichi-ken, JP) ; Hattori; Makoto; ( Aichi-ken,
JP) ; Takashige; Takayuki; (Aichi-ken, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW, SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
MITSUBISHI HEAVY INDUSTRIES,
LTD.
Tokyo
JP
|
Family ID: |
40667314 |
Appl. No.: |
12/300725 |
Filed: |
June 24, 2008 |
PCT Filed: |
June 24, 2008 |
PCT NO: |
PCT/JP2008/061490 |
371 Date: |
March 26, 2009 |
Current U.S.
Class: |
417/44.11 |
Current CPC
Class: |
F04B 49/065 20130101;
F04B 2203/0205 20130101; H02P 29/60 20160201; F04B 2201/0403
20130101; F04B 2203/0201 20130101; F04B 2203/0208 20130101; F04B
2203/0207 20130101; H02P 29/032 20160201; F04B 49/10 20130101 |
Class at
Publication: |
417/44.11 |
International
Class: |
F04B 49/06 20060101
F04B049/06 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 22, 2007 |
JP |
2007-302605 |
Claims
1. An electric compressor characterized by comprising: a
compression mechanism that sucks in a refrigerant and compresses
and discharges the refrigerant; an electric motor that drives said
compression mechanism; a casing that houses said compression
mechanism and said electric motor; a control portion that is housed
in said casing and controls to drive said electric motor; a
temperature detector that detects a temperature of one or more
components that constitute one or both of said control portion and
said electric motor; and a current detector that detects a current
flowing through said component, wherein when the temperature
detected by said temperature detector is a temperature Td, the
current detected by said current detector when said temperature
detector detects said temperature Td is a current Id, and a current
corresponding to said temperature Td at a temperature
characteristic relating to the current specific to said component
is a current Ia(Td), said control portion stops driving said
electric motor on the basis of a result of comparison between
Ia(Td) and Id.
2. The electric compressor according to claim 1, characterized in
that when the current corresponding to said temperature Td is a
current Ib(Td) at a reduced temperature characteristic with a lower
current at each temperature than the temperature characteristic
relating to the current specific to said component, said control
portion controls to stop driving said electric motor when
Ia(Td).ltoreq.Id, and performs protection control to reduce a load
of said electric motor when Ib(Td).ltoreq.Id<Ia(Td).
3. The electric compressor according to claim 1, characterized in
that when the current corresponding to said temperature Td is a
current Ib(Td) at a reduced temperature characteristic with a lower
current at each temperature than the temperature characteristic
relating to the current specific to said component, said control
portion controls to stop driving said electric motor when
Ia(Td).ltoreq.Id, and performs protection control to increase a
rotational speed of said electric motor when
Ib(Td).ltoreq.Id<Ia(Td) and the rotational speed of said
electric motor is a predetermined rotational speed x or lower.
4. The electric compressor according to claim 1, characterized in
that when the current corresponding to said temperature Td is a
current Ib(Td) at a reduced temperature characteristic with a lower
current at each temperature than the temperature characteristic
relating to the current specific to said component, said control
portion controls to stop driving said electric motor when
Ia(Td).ltoreq.Id, and performs protection control to reduce the
rotational speed of said electric motor when
Ib(Td).ltoreq.Id<Ia(Td) and the rotational speed of said
electric motor exceeds a predetermined rotational speed y.
5. The electric compressor according to claim 1, characterized in
that when said component is a switching element for said electric
motor provided in said control portion, and the current
corresponding to said temperature Td is a current Ib(Td) at a
reduced temperature characteristic with a lower current at each
temperature than the temperature characteristic relating to the
current specific to said component, said control portion controls
to stop driving said electric motor when Ia(Td).ltoreq.Id, and
performs protection control to reduce a carrier frequency that
controls on/off of said switching element when
Ib(Td).ltoreq.Id<Ia(Td).
6. The electric compressor according to any of claims 2 to 5,
characterized in that when the current corresponding to said
temperature Td is a current Ic(Td) (where Ic(Td)<Ib(Td)) at a
reduced temperature characteristic with a lower current at each
temperature than the temperature characteristic relating to the
current specific to said component, said control portion releases
said protection control when Id.ltoreq.Ic(Td).
7. An electric compressor characterized by comprising: a
compression mechanism that sucks in a refrigerant and compresses
and discharges the refrigerant; an electric motor that drives said
compression mechanism; a casing that houses said compression
mechanism and said electric motor; a control portion that is housed
in said casing and controls to drive said electric motor; a
temperature detector that detects a temperature of one or more
components that constitute one or both of said control portion and
said electric motor; and an electric power detector that detects
electric power flowing through said component, wherein when the
temperature detected by said temperature detector is a temperature
Td, the electric power detected by said electric power detector
when said temperature detector detects said temperature Td is
electric power Pd, and electric power corresponding to said
temperature Td at a temperature characteristic relating to the
electric power specific to said component is electric power Pa(Td),
said control portion controls to stop driving said electric motor
on the basis of a result of comparison between Pa(Td) and Pd.
8. The electric compressor according to claim 7, characterized in
that when the electric power corresponding to said temperature Td
is electric power Pb(Td) at a reduced temperature characteristic
with lower electric power at each temperature than the temperature
characteristic relating to the electric power specific to said
component, said control portion controls to stop driving said
electric motor when Pa(Td).ltoreq.Pd, and performs protection
control to reduce a load of said electric motor when
Pb(Td).ltoreq.Pd<Pa(Td).
9. The electric compressor according to claim 7, characterized in
that when the electric power corresponding to said temperature Td
is electric power Pb(Td) at a reduced temperature characteristic
with lower electric power at each temperature than the temperature
characteristic relating to the electric power specific to said
component, said control portion controls to stop driving said
electric motor when Pa(Td).ltoreq.Pd, and performs protection
control to increase a rotational speed of said electric motor when
Pb(Td).ltoreq.Pd<Pa(Td) and the rotational speed of said
electric motor is a predetermined rotational speed x or lower.
10. The electric compressor according to claim 7, characterized in
that when the electric power corresponding to said temperature Td
is electric power Pb(Td) at a reduced temperature characteristic
with lower electric power at each temperature than the temperature
characteristic relating to the electric power specific to said
component, said control portion controls to stop driving said
electric motor when Pa(Td).ltoreq.Pd, and performs protection
control to reduce the rotational speed of said electric motor when
Pb(Td).ltoreq.Pd<Pa(Td) and the rotational speed of said
electric motor exceeds a predetermined rotational speed y.
11. The electric compressor according to claim 7, characterized in
that when said component is a switching element for said electric
motor provided in said control portion, and the electric power
corresponding to said temperature Td is electric power Pb(Td) at a
reduced temperature characteristic with lower electric power at
each temperature than the temperature characteristic relating to
the electric power specific to said component, said control portion
controls to stop driving said electric motor when Pa(Td).ltoreq.Pd,
and performs protection control to reduce a carrier frequency that
controls on/off of said switching element when
Pb(Td).ltoreq.Pd<Pa(Td).
12. The electric compressor according to any of claims 7 to 11,
characterized in that when the electric power corresponding to said
temperature Td is electric power Pc(Td) (where Pc(Td)<Pb(Td)) at
a reduced temperature characteristic with lower electric power at
each temperature than the temperature characteristic relating to
the electric power specific to said component, said control portion
releases said protection control when Pd.ltoreq.Pc(Td).
Description
TECHNICAL FIELD
[0001] The present invention relates to an electric compressor in
which an electric motor that drives a compression mechanism and a
control apparatus that controls the electric motor are integrated
with the compression mechanism, and more particularly to an
electric compressor that can prevent heat damage to a high voltage
component such as a switching element provided in the control
apparatus.
BACKGROUND ART
[0002] A vehicle-mounted air conditioner in an electric vehicle or
a fuel cell vehicle with no engine has a compressor including an
electric motor as a power source for compressing and circulating a
refrigerant. Since the electric motor needs to be rotated at a
desired rotational speed according to a command from a main control
apparatus of the air conditioning apparatus, a separate control
apparatus is required. This control apparatus includes an
electrical circuit or an electronic circuit. Specifically, the
control apparatus includes electronic elements such as a central
processing unit and a memory, and also a switching element (power
transistor element) such as an IGBT (Insulated Gate Bipolar
Transistor) or an FET (Field Effect Transistor) for constituting a
so-called inverter circuit (switching circuit). There is an
electric compressor in which the control apparatus, a compression
mechanism, and an electric motor are incorporated into one casing
for saving space. Hereinafter, this electric compressor is
sometimes referred to as an integrated electric compressor.
[0003] The switching element has a function of supplying large
electric power to the electric motor and controlling the rotational
speed of the electric motor. However, the control by the control
apparatus is to control the electric motor to rotate at a desired
rotational speed according to the command from the main control
apparatus. During the control, power consumption becomes too high,
and an overcurrent sometimes flows that may damage a high voltage
component (hereinafter sometimes simply referred to as component)
mounted in the control apparatus of the integrated electric
compressor. Thus, the switching element and other components are
increased in temperature and damaged (heat damage). In an extreme
case, it is supposed that the components rupture or catch fire. The
heat damage may occur to components that constitute the electric
motor.
[0004] Patent Documents 1 and 2 propose protecting a control
apparatus of an integrated electric compressor from heat
damage.
[0005] Patent Document 1 proposes an electric compressor
integratedly including a compression mechanism that sucks in and
compresses a refrigerant, an electric motor that drives the
compression mechanism, and an electrical circuit that controls a
rotational speed of the electric motor, wherein the compressor
includes protection control means for increasing a rotational speed
of the compression mechanism, that is, a rotational speed of the
electric motor when a temperature of the electrical circuit exceeds
a predetermined temperature, and further when an actual rotational
speed of the compression mechanism is a predetermined rotational
speed or lower.
[0006] This proposal is based on the following findings.
Specifically, when the rotational speed of the compression
mechanism is relatively low, a cooling effect by the refrigerant
falls below calorific values of the electrical circuit and the
electric motor, and thus the cooling effect by the refrigerant
increases with increasing rotational speed. On the other hand, when
the rotational speed of the compression mechanism is relatively
high, the calorific values of the electrical circuit and the
electric motor exceed the cooling effect by the refrigerant, and
thus the temperatures of the electrical circuit and the electric
motor compression mechanism increase with increasing rotational
speed. Thus, in Patent Document 1, when the temperature of the
electrical circuit exceeds the predetermined temperature, the
rotational speed of the compression mechanism is increased to
reduce the temperatures of the electric motor and the electrical
circuit.
[0007] Patent Document 2 is based on the findings that a larger
amount of refrigerant to be compressed is circulated at higher
rotational speeds of an electric compressor, and in combination
with an increasing cooling effect of a switching element by the
refrigerant, an electric motor of the electric compressor has a
larger current margin in a certain rotational speed region than in
other regions (paragraph [0025] in Patent Document 2).
Specifically, Patent Document 2 proposes a control apparatus for an
electric compressor including a rotational speed limit control
portion that maintains a rotational speed of an electric motor
within a rotational speed between predetermined upper and lower
limit rotational speeds in the case where a certain condition A
relating to an inverter output current or a switching element
temperature that indicates a state that requires protection of the
switching element that constitutes a control apparatus of an
integrated electric compressor irrespective of an electric motor
rotational speed command from a main control apparatus of an air
conditioning apparatus.
[0008] In Patent Document 2, for example, it is determined whether
an actual operation rotational speed of the electric compressor is
lower than a predetermined rotational speed N1 when a maximum value
of an inverter output current absolute value during one second
becomes higher than 0.9 times a known rated current of the
switching element. When the actual operation rotational speed is
lower than the rotational speed N1, a current margin is small, and
thus the rotational speed is increased by a predetermined
rotational speed N3. When the actual operation rotational speed is
higher than N1 and also higher than N2, the current margin is also
small, and thus the rotational speed is reduced by a predetermined
rotational speed N4. Then, it is determined whether a rotational
speed control operation needs to be continued.
[0009] Patent Document 1: Japanese Patent Laid-Open No.
2004-68807
[0010] Patent Document 2: Japanese Patent Laid-Open No.
2007-92636
DISCLOSURE OF THE INVENTION
[0011] In Patent Document 1, actually, it is determined which of
three temperature regions A, E and D (FIG. 4(a) in Patent Document
1) a temperature Ti of the electrical circuit falls within, and
details of control of the compression mechanism (electric motor) is
determined according to each temperature region. Thus, for example,
there is a risk that protection control to stop the electric motor
or the like is performed when not necessary at the temperature Ti
in terms of a temperature characteristic of the electrical circuit.
Specifically, in Patent Document 1, protection control cannot be
performed according to a capability of a component to be protected
from heat damage. The protection control should be minimized
because it may diminish comfortable feelings of a driver and a
passenger due to air conditioning.
[0012] In Patent Document 2, a standard of 0.9 times the rated
current of the switching element is used, but a temperature is
still not considered.
[0013] The present invention is achieved on the basis of such
technical problems, and has an object to provide an electric
compressor that can protect a component to be protected from heat
damage according to a capability of the component.
[0014] FIGS. 3A and 3B respectively show temperature
characteristics of a current and electric power of a component. As
shown in FIGS. 3A and 3B, the component can generally use a current
and electric power up to a maximum absolute rated current and
maximum absolute rated electric power at room temperature or lower,
but usable current and electric power decrease with increasing
temperature. A high current and a high voltage are passed through
the component, and if a current and electric power higher than a
current (allowable current) and electric power (allowable electric
power) specified at each temperature as shown in FIGS. 3A and 3B
are used, the temperature increases to cause heat damage.
[0015] Thus, the present invention provides an electric compressor
characterized by including: a compression mechanism that sucks in a
refrigerant and compresses and discharges the refrigerant; an
electric motor that drives the compression mechanism; a casing that
houses the compression mechanism and the electric motor; a control
portion that is housed in the casing and controls to drive the
electric motor; a temperature detector that detects a temperature
of one or more components that constitute one or both of the
control portion and the electric motor; and a current detector that
detects a current flowing through the component, wherein the
electric compressor protects the component from heat damage in the
following manners. Specifically, when the temperature detected by
the temperature detector is a temperature Td, the current detected
by the current detector when the temperature detector detects the
temperature Td is a current Id, and a current corresponding to the
temperature Td at a temperature characteristic relating to the
current specific to the component is a current Ia(Td), the control
portion stops driving the electric motor on the basis of a result
of comparison between Ia(Td) and Id.
[0016] The electric compressor of the present invention compares
the temperature characteristic of the component and the detected
temperature Td and current Id to stop driving the electric motor,
thereby allowing the component to be protected from heat damage
according to a capability of the component.
[0017] In the electric compressor of the present invention, when
the current corresponding to the temperature Td is a current Ib(Td)
at a reduced temperature characteristic with a lower current at
each temperature than the temperature characteristic relating to
the current specific to the component, the control portion controls
to stop driving the electric motor when Ia(Td).ltoreq.Id. There is
a high risk that the component is subjected to heat damage, and
thus the electric motor is stopped to reduce the temperature of the
component.
[0018] When Ib(Td).ltoreq.Id<Ia(Td), the control portion
controls to reduce a load of the electric motor. The load of the
electric motor is reduced to reduce the temperature of the
component of the electric motor, and also reduce the temperature of
the component that constitutes the control portion because the
flowing current is reduced. Thus, the component is protected from
heat damage. The control when Ib(Td).ltoreq.Id<Ia(Td) is
referred to as protection control.
[0019] The protection control may be performed so as to reduce the
load of the electric motor, and also to increase a rotational speed
of the electric motor when the rotational speed of the electric
motor is a predetermined rotational speed x or lower, thereby
reducing the temperatures of the component of the electric motor
and the component that constitutes the control portion. When the
rotational speed of the electric motor exceeds a predetermined
rotational speed y, the control may be performed so as to reduce
the rotational speed of the electric motor, thereby reducing the
temperatures of the component of the electric motor and the
component that constitutes the control portion. This is based on
the above described findings.
[0020] When the component to be protected from heat damage is a
switching element for the electric motor provided in the control
portion, the protection control is performed so as to reduce a
carrier frequency that controls on/off of the switching element.
The carrier frequency may be reduced to reduce a calorific value of
the switching element.
[0021] In the electric compressor of the present invention, when
the current corresponding to the temperature Td is a current Ic(Td)
(where Ic(Td)<Ib(Td)) at a reduced temperature characteristic
with a lower current at each temperature than the temperature
characteristic relating to the current specific to the component,
the control portion can release the protection control when Id
Ic(Td).
[0022] The present invention may include an electric power detector
in place of the current detector, and when a temperature detected
by a temperature detector is a temperature Td, electric power
detected by the electric power detector when the temperature
detector detects the temperature Td is electric power Pd, and
electric power corresponding to the temperature Td at a temperature
characteristic relating to the electric power specific to the
component is electric power Pa(Td), the control portion may stop
driving the electric motor on the basis of a result of comparison
between Pa(Td) and Pd.
[0023] This electric compressor can also perform and release the
above described protection control. In this case, Id, Ia(Td),
Ib(Td) and Ic(Td) are replaced by Pd, Pa(Td), Pb(Td) and
Pc(Td).
[0024] According to the present invention, the temperature
characteristic of the component and the detected temperature Td and
current Id (electric power Pd) are compared to stop driving the
electric motor, thereby allowing the component to be protected from
heat damage according to a capability of the component.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a schematic view of a configuration of a vapor
compression refrigerator using an electric compressor according to
an embodiment;
[0026] FIG. 2 is a block diagram of a configuration of a control
portion of the electric compressor according to the embodiment;
[0027] FIG. 3A is a graph showing a temperature characteristic of a
current of a component to be protected from heat damage;
[0028] FIG. 3B is a graph showing a temperature characteristic of
an electric power of a component to be protected from heat
damage;
[0029] FIG. 4A is a graph showing temperature characteristic data
of a current held by a second control portion;
[0030] FIG. 4B is a graph showing temperature characteristic data
of an electric power held by a second control portion; and
[0031] FIG. 5 is a flowchart showing a procedure of protection
control of the electric compressor according to the embodiment.
DESCRIPTION OF SYMBOLS
[0032] 1 . . . vapor compression refrigerator for vehicle [0033] 10
. . . electric compressor [0034] 11 . . . compression mechanism
[0035] 12 . . . electric motor [0036] 13 . . . control portion
[0037] 13a . . . first control portion [0038] 13b . . . second
control portion [0039] 14 . . . temperature detector [0040] 15 . .
. current detector [0041] 20 . . . condenser [0042] 21 . . .
cooling fan [0043] 30 . . . receiver [0044] 40 . . . expansion
valve [0045] 50 . . . evaporator [0046] 51 . . . blower [0047] 52 .
. . inside and outside air switching damper [0048] 60 . . . main
control unit
BEST MODE FOR CARRYING OUT THE INVENTION
[0049] Now, an embodiment of the present invention will be
described in detail with reference to the accompanying
drawings.
[0050] The embodiment is applied to an electric compressor of a
vapor compression refrigerator for a vehicle (an air conditioning
apparatus for a vehicle), and FIG. 1 is a schematic view of a
configuration of a vapor compression refrigerator for a vehicle 1
using an electric compressor 10 according to the embodiment.
[0051] As shown in FIG. 1, the vapor compression refrigerator 1
includes the electric compressor 10 that compresses a refrigerant
into a refrigerant of high temperature and pressure; a condenser 20
that cools and condenses the high temperature and pressure
refrigerant; a receiver 30 that performs gas-liquid separation of
the refrigerant from the condenser 20; an expansion valve 40 that
reduces pressure of the cooled high pressure refrigerant; and an
evaporator 50 that evaporates the low pressure refrigerant with
reduced pressure to exhibit a refrigeration capability. These
components are connected in series by pipes P. The vapor
compression refrigerator 1 also includes a main control unit 60
that controls operation of the electric compressor 10 and the
condenser 20 or the like on the basis of an air conditioning
load.
[0052] The electric compressor 10 includes a compression mechanism
11 that sucks in the refrigerant and compresses and discharges the
refrigerant, an electric motor 12 that drives the compression
mechanism 11, and a control portion 13 including an inverter
circuit that controls to drive the electric motor 12. For example,
a scroll compressor can be used as the compression mechanism 11, a
DC brushless electric motor can be used as the electric motor 12,
and the compression mechanism 11 and the electric motor 12 are
integrated coaxially and in series.
[0053] The electric compressor 10 includes a casing (not shown)
that houses the compression mechanism 11, the electric motor 12,
and the control portion 13. The electric compressor 10 is
configured so that the refrigerant discharged from the evaporator
50 and sucked into the casing of the electric compressor 10 cools
the control portion 13, is then sucked and compressed by the
compression mechanism 11, and then cools the electric motor 12 and
is discharged toward the condenser 20.
[0054] As shown in FIG. 2, the control portion 13 includes a first
control portion 13a and a second control portion 13b. The first
control portion 13a controls a predetermined current (voltage) to
be supplied to the electric motor 12 on the basis of a command from
the main control unit 60. The second control portion 13b provides
protection determination and a command based thereon to the first
control portion 13a. Though not shown in FIG. 2, the control
portion 13 includes components such as a switching element, a
capacitor, an inductor, or the like that constitute the inverter
circuit, and the first control portion 13a and the second control
portion 13b control operation of the switching element. In this
example, the first control portion 13a and the second control
portion 13b are separated, but for example, physically one
microcomputer may have functions of the above described two control
portions.
[0055] The electric compressor 10 includes a temperature detector
14 that detects a temperature Td of the switching element (for
example, IGBT) mounted in the control portion 13. The electric
compressor 10 also includes a current detector 15 that detects a
current Id flowing through the switching element. The temperature
Td detected by the temperature detector 14 is provided to the
second control portion 13b. The current Id detected by the current
detector 15 is also provided to the second control portion 13b, The
second control portion 13b performs protection control to protect
the switching element from heat damage on the basis of the
temperature Td and the current Id. The protection control is
performed irrespective of the command from the main control unit
60. In some cases, the main control unit 60 operates for performing
the protection control. The details of the control will be
described later.
[0056] The refrigerant compressed into the refrigerant of high
temperature and pressure by the electric compressor 10 (compression
mechanism 11) is introduced into the condenser 20. The condenser 20
includes a cooling fan 21 that supplies outside air to the
condenser 20. The high temperature and pressure refrigerant
introduced into the condenser 20 is cooled by the outside air
supplied by the cooling fan 21, condensed and liquefied, and fed to
the receiver 30. The cooling fan 21 is generally controlled in
operation by the main control unit 60 according to an air
conditioning load, but sometimes operates during protection control
as described later.
[0057] The receiver 30 performs gas-liquid separation of the
refrigerant received from the condenser 20. The separated liquid
refrigerant is fed to the expansion valve 40. The receiver 30 also
stores an excess liquid refrigerant in the vapor compression
refrigerator for a vehicle 1.
[0058] The high pressure liquid refrigerant received from the
receiver 30 is reduced in pressure by the expansion valve 40 into a
low-temperature two-phase state, and fed to the evaporator 50.
[0059] The evaporator 50 includes a blower 51 and an inside and
outside air switching damper 52. The blower 51 drive-controlled by
the main control unit 60 supplies outside air or in-vehicle
circulation air (inside air) to the evaporator 50 according to a
position of the inside and outside air switching damper 52. The
refrigerant in the low-temperature two-phase state introduced into
the evaporator 50 is subjected to heat exchange (heat absorption)
with the outside air or the inside air to again become a gas
refrigerant and sucked by the electric compressor 10 (compression
mechanism 11). The gas refrigerant is relatively low in
temperature, and cools the control portion 13 and the electric
motor 12 of the electric compressor 10 as described above.
[0060] Next, protection control performed by the control portion 13
and the main control unit 60 will be described. The protection
control is performed for protecting the switching element provided
in the control portion 13 from heat damage. The component to be
protected from heat damage is herein limited to the switching
element for description, but it is understood that the present
invention may be applied to any of components included in the
control portion 13 and the electric motor 12.
[0061] FIG. 4A shows a graph showing data on the switching element
held by the second control portion 13b plotted on a coordinate with
the temperature Tc(.degree. C.) on the axis of abscissa and the
allowable current (A) on the axis of ordinate. As shown in FIG. 4A,
the second control portion 13b holds three types of data. One is
temperature characteristic data a of the switching element. The
temperature characteristic data a is specific to the actually used
switching element. The second control portion 13b also holds
reduced temperature characteristic data b and reduced temperature
characteristic data c besides the temperature characteristic data
a. As shown in FIG. 4B, the data on the temperature characteristic
may relate to a relationship between the temperature Tc and
allowable electric power (W).
[0062] At the same temperature, an allowable current Ia(Td) of the
temperature characteristic data a of the switching element, an
allowable current Ib(Td) of the reduced temperature characteristic
data b, and an allowable current Ic(Td) of the reduced temperature
characteristic data c have a relationship of
Ic(Td)<Ib(Td)<Ia(Td).
[0063] The allowable current Ib(Td) at room temperature (20.degree.
C.) or less of the reduced temperature characteristic data b is set
to, for example, about 90% of the allowable current Ia(Td) of the
temperature characteristic data a of the switching element. The
allowable current Ic(Td) at room temperature (20.degree. C.) or
less of the reduced temperature characteristic data c is set to,
for example, about 85% of the allowable current Ia(Td) of the
temperature characteristic data a of the switching element. At a
temperature at which the allowable current Ia(Td) of the
temperature characteristic data a of the switching element is zero,
the allowable current Ib(Td) of the reduced temperature
characteristic data b and the allowable current Ic(Td) of the
reduced temperature characteristic data c are both set to zero.
[0064] FIG. 5 is a flowchart showing a procedure of the protection
control by the second control portion 13b. It is supposed that the
vapor compression refrigerator 1 is operated by the control by the
main control unit 60 according to an air conditioning load. This
control will be hereinafter referred to as normal control.
[0065] The second control portion 13b obtains data on the current
Id flowing through the switching element detected by the current
detector 15, and data on the temperature Td of the switching
element detected by the temperature detector 14 (S100 in FIG. 5).
In FIG. 5, there is a mention of electric power Pd, which means
that the electric power Pd supplied to the switching element may be
used in place of the current Id, or the electric power Pd may be
used together with the current Id. In the description below, the
current Id only will be referred to.
[0066] When obtaining data on the detected current Id and
temperature Td, the second control portion 13b compares the data
with the temperature characteristic data a of the switching
element, the reduced temperature characteristic data b, and the
reduced temperature characteristic data c (S110 in FIG. 5).
Specifically, the current Ia(Td) corresponding to the temperature
Td in the temperature characteristic data a, the current Ib(Td)
corresponding to the temperature Td in the reduced temperature
characteristic data b, and the current Ic(Td) corresponding to the
temperature Td in the reduced temperature characteristic data c are
compared. The result of comparison is classified into the following
three categories:
[0067] Id.gtoreq.Ia(Td)
[0068] Id<Ib(Td)
[0069] Ib(Td).ltoreq.Id<Ia(Td)
[0070] When the result of comparison is Id.gtoreq.la(Td), the
second control portion 13b determines that the switching element is
subjected to heat damage. Thus, the second control portion 13b
stops supplying the current to the electric motor 12 to stop
operation of the electric motor 12 irrespective of the command from
the main control unit 60 (S150 in FIG. 5). Then, a communication
system provided in the control portion 13 transmits information on
the stop of the supply of the current to the electric motor 12 to
the main control unit 60 (S152 in FIG. 5), and then a command from
the main control unit 60 is waited (S154 in FIG. 5).
[0071] At this time, operation of the cooling fan 21 attached to
the condenser 20 and the blower 51 attached to the evaporator 50 is
preferably continued. This is for preventing reduction in
comfortable feelings due to air conditioning caused by the stop of
the electric motor 12 as much as possible.
[0072] When the result of comparison is Id<Ib(Td), the normal
control is continued without performing the protection control
(S160 in FIG. 5). When Id<Ib(Td), the second control portion 13b
determines that there is a margin until the allowable current is
reached and there is no risk of heat damage to the switching
element.
[0073] When the result of comparison is Ib(Td).ltoreq.Id<Ia(Td),
the second control portion 13b performs the protection control
(S120 in FIG. 5). Ib(Td).ltoreq.Id<Ia(Td) indicates, in FIG. 4A,
that the detected current Id falls between a curve for the
temperature characteristic data a and a curve for the reduced
temperature characteristic data b. In this case, it is determined
that there is a risk of heat damage to the switching element, and
the protection control is performed.
[0074] The protection control is selected from one or a combination
of two or more of (I) to (IV) described below.
[0075] (I) Reduce Electric Motor Torque
[0076] Torque (load) applied to the electric motor 12 is reduced to
reduce the current flowing through the switching element of the
control portion 13 and supplied to the electric motor 12. The ratio
of discharge pressure to suction pressure of the refrigerant in the
compression mechanism 11 is reduced to reduce the torque applied to
the electric motor 12. To reduce the ratio of discharge pressure to
suction pressure, it is only necessary that the discharge pressure
is reduced or the suction pressure is increased in the following
manners.
[0077] Reduction in Discharge Pressure
[0078] When a capability (an amount of heat dissipation) of the
condenser 20 is increased, the discharge pressure of the
compression mechanism 11 can be reduced. Specifically, a rotational
speed of the cooling fan 21 is increased to increase an amount of
wind passing through the condenser 20, thereby increasing the
capability of the condenser 20. The main control unit 60 provides
an instruction to increase the rotational speed of the cooling fan
21 to the cooling fan 21 on the basis of an instruction from the
second control portion 13b.
[0079] Increase in Suction Pressure
[0080] When air to the evaporator 50 is introduced from outside
air, the inside and outside air switching damper 52 is activated to
circulate air in the vehicle (inside air). Then, heat exchange can
be facilitated to increase the suction pressure of the compression
mechanism 11.
[0081] When a capability (an amount of heat absorption) of the
evaporator 50 is reduced, the suction pressure of the compression
mechanism 11 can be increased. Specifically, a rotational speed of
the blower 51 is reduced to reduce an amount of wind passing
through the evaporator 50, thereby reducing the capability of the
evaporator 50. The reduction in the amount of wind to the
evaporator 50 may reduce comfortable feelings due to air
conditioning, and an amount of reduction needs to be limited to
some extent.
[0082] Further, there is a system (dual system) in which two
evaporators 50 are provided in the vehicle and placed in parallel
on a refrigeration cycle circuit. In the dual system, the two
evaporators 50 generally include a large evaporator having a
relatively large capability and a small evaporator having a
relatively small capability. The large evaporator is for a front
seat of the vehicle, and the small evaporator is for a rear part of
the vehicle. In the dual system, a rotational speed of a blower
attached to the small evaporator provided in the rear part of the
vehicle may be reduced, and a rotational speed of a blower attached
to the large evaporator may be reduced later as required.
[0083] (II) Increase Rotational Speed of Compression Mechanism
11
[0084] When a rotational speed of the compression mechanism 11,
that is, a rotational speed of the electric motor 12 is a
predetermined rotational speed x or lower, the rotational speed of
the compression mechanism 11 is increased.
[0085] When the rotational speed is relatively low, a cooling
effect by the refrigerant falls below a calorific value of the
control portion 13 including the switching element, and thus the
cooling effect by the refrigerant increases with increaing
rotational speed. On the other hand, when the rotational speed is
relatively high, the calorific value of the control portion 13
exceeds the cooling effect by the refrigerant, and thus the
temperature of the control portion 13 increases with increasing
rotational speed. It is understood that the rotational speed of the
electric motor 12 needs only to be increased to increase the
rotational speed of the compression mechanism 11.
[0086] Thus, when the rotational speed of the compression mechanism
11 is the predetermined rotational speed x or lower, the rotational
speed is increased to reduce the temperatures of the electric motor
12 and the control portion 13, thereby allowing the switching
element to be effectively protected from heat damage. The case
where the rotational speed is the predetermined rotational speed x
or lower is synonymous with the case where the rotational speed is
relatively low. The predetermined rotational speed x can be
specified by previously checking a condition that the cooling
effect by the refrigerant falls below the calorific value of the
control portion 13 including the switching element.
[0087] (III) Reduce Rotational Speed of Compression Mechanism
11
[0088] When the rotational speed of the compression mechanism 11,
that is, the rotational speed of the electric motor 12 is a
predetermined rotational speed y or higher, the rotational speed of
the compression mechanism 11 is reduced.
[0089] As described above, when the rotational speed of the
compressor is relatively high, the calorific value of the control
portion 13 exceeds the cooling effect by the refrigerant, and thus
the temperature of the control portion 13 increases with increasing
rotational speed.
[0090] Thus, when the rotational speed of the compression mechanism
11 is the predetermined rotational speed y or higher, the
rotational speed is reduced to reduce the temperatures of the
electric motor 12 and the control portion 13, thereby allowing the
switching element to be effectively protected from heat damage. The
case where the rotational speed is the predetermined rotational
speed y or higher is synonymous with the case where the rotational
speed is relatively high. The predetermined rotational speed y can
be specified by previously checking a condition that the calorific
value of the control portion 13 exceeds the cooling effect by the
refrigerant.
[0091] (IV) Reduce Carrier Frequency
[0092] When the switching element is, for example, an IGBT, an
on/off cycle of the IGBT is controlled by a carrier frequency. The
carrier frequency is reduced to reduce a calorific value of the
IGBT. Thus, the carrier frequency is reduced to allow the IGBT
(switching element) to be effectively protected from heat damage.
The control of the carrier frequency is performed by the first
control portion 13a in the normal control, and performed by the
first control portion 13a on the basis of the instruction from the
second control portion 13b in the protection control.
[0093] The second control portion 13b performs temporal
differentiation of the current Id (dI/dt) while continuously
detecting the current Id flowing through the switching element
after performing the protection control.
[0094] The second control portion 13b determines whether a value of
the temporal differentiation of the current Id is positive
(dI/dt.gtoreq.0) or not (dI/dt<0) (S130 in FIG. 5). When the
current Id supplied to the electric motor 12 increases with time or
does not change, dI/dt.gtoreq.0. When the current Id supplied to
the electric motor 12 decreases with time, dI/dt<0.
[0095] When dI/dt.gtoreq.0, the second control portion 13b
determines whether Id.gtoreq.Ia(Td) using the temperature Td and
the current Id continuously detected, and the current Ia(Td)
corresponding to the temperature Td in the temperature
characteristic data a of the switching element (S140 in FIG.
5).
[0096] When Id.gtoreq.Ia(Td), the second control portion 13b stops
supplying the electric power to the electric motor 12 to stop
operation of the compression mechanism 11 (S150 in FIG. 5). Then,
the second control portion 13b transmits information on the stop of
the supply of the current to the electric motor 12 to the main
control unit 60 (S152 in FIG. 5), and then a command from the main
control unit 60 is waited (S154 in FIG. 5).
[0097] When Id<Ia(Td), the protection control (S120) is
continued, the second control portion 13b determines in S130
whether the value of the temporal differentiation of the current Id
is positive (dI/dt.gtoreq.0) or not (dI/dt<0), and the above
described procedure is performed on the basis of the result.
[0098] When dI/dt<0, the second control portion 13b determines
whether Id.ltoreq.Ic(Td) using the temperature Td and the current
Id continuously detected, and the current Ic(Td) corresponding to
the temperature Td in the reduced temperature characteristic data c
(S170 in FIG. 5). When Id.ltoreq.Ic(Td), the control by the second
control portion 13b is released to return to the normal control
(S180 in FIG. 5). When Id>Ic(Td), the protection control (S120)
is continued, the second control portion 13b determines in S130
whether the value of the temporal differentiation of the current Id
is positive (dI/dt.gtoreq.0) or not (dI/dt<0), and the above
described procedure is performed on the basis of the result.
[0099] The above described control procedure will be summarized
below.
[0100] (1) It is determined in S110 whether the compression
mechanism 11 is stopped (S150 in FIG. 5), the normal control is
continued without performing the protection control (S160 in FIG.
5), or the protection control is performed (S120 in FIG. 5).
[0101] (2) When the protection control is performed (S120 in FIG.
5), it is determined whether the current Id flowing through the
switching element tends to increase (including the case of no
change) or tends to decrease (S130 in FIG. 5).
[0102] When the current Id tends to increase, it is determined in
S140 whether the compression mechanism 11 is stopped (S150 in FIG.
5), or the protection control is again performed (S120 in FIG. 5).
When the current Id tends to decrease, it is determined whether the
protection control can be stopped to return to the normal control
(S170 in FIG. 5).
[0103] Thus, the control procedure is advanced so as to return to
the normal control or stop the compression mechanism 11 when the
protection control is performed.
[0104] As described above, in the embodiment, the temperature
characteristic data a on the allowable current of the switching
element, the temperature Td of the switching element, and the
current Id flowing through the switching element are compared to
determine the control procedure thereafter. Thus, in the
embodiment, the current Id and the temperature characteristic data
a are compared, and the operation of the compression mechanism 11
can be stopped only when the switching element is actually
subjected or highly likely to be subjected to heat damage at the
temperature in stopping the operation of the compression mechanism
11. Specifically, the switching element can be effectively
protected from heat damage while making the most of the capability
of the switching element. On the other hand, in control in which a
temperature region is determined and operation of a compression
mechanism 11 is stopped when a temperature Td of a switching
element falls within the temperature region as in Patent Document
1, the operation of the compression mechanism 11 is stopped even
when, for example, there is little risk of heat damage to the
switching element. This can be easily understood by plotting the
temperature region in an overlapping manner on the graph in FIG.
3A.
[0105] In the above description, the high voltage component to be
protected from heat damage is the switching element, but the high
voltage component of the present invention is not limited to this.
The control portion 13 includes the components such as the inductor
and the capacitor besides the switching element, and the present
invention may be widely applied to these components. The present
invention may be applied to the components included in the electric
motor 12 that rotationally drives the compression mechanism 11.
[0106] In the above description, the temperature characteristic
data a, the reduced temperature characteristic data b, and the
reduced temperature characteristic data c relate to the current,
but not limited to the current, the data may relate to electric
power in the present invention. The electric power may be used
according to a type of a component to be protected from heat
damage. For the control procedure in this case, it is only
necessary that Id, Ia(Td), Ib(Td), Ic(Td) and dI/dt in FIG. 5 may
be replaced by Pd, Pa(Td), Pb(Td), Pc(Td) and dP/dt, respectively.
Both the current and voltage may be used.
* * * * *